The invention relates generally to power transmission and more specifically to a system and method for transmitting direct current electrical power to marine or subsea electrical equipment.
In the last few decades, the field of power conversion has grown tremendously due to its imminent advantages in motor drives, renewable energy systems, high voltage direct current (HVDC) systems, and the like. For example, a subsea oil and gas production system which requires hundreds of megawatts of electric power may employ a HVDC transmission and distribution system for delivery of electric power. Furthermore, in recent time, marine traffic has also increased substantially across the world due to tremendous rise in cargo transport vessels, warships, offshore oil ships, passenger ships etc. These vessels or ships have many electrical loads on board. Variable speed electric drives for pumps, fans, electric propulsion installations, lighting and air conditioning are some examples of the electrical loads on board of a ship.
Often subsea and marine power supply circuit arrangements include a direct current (DC) power system including a DC bus to which a plurality of power converters and a plurality of loads are connected. Power converters supply energy to the plurality of loads via the common DC bus. The common DC bus also includes a plurality of capacitors. Such a power system poses significant protection problems due to a large number of subsystems in the circuit. In many cases, the common DC bus itself may be divided in a plurality of subsections and the relevant subsections then further form subsystems. The protection problems are exacerbated by the subsea environment and the customer requests of system availability for several years without maintenance. It is therefore necessary to design the overall set of subsystems connected to the common DC bus in a way that limits the damages when even just one of the subsystem fails because of a short-circuit fault. The main problem is discharge of large quantity of energy accumulated in the capacitors that are connected to the common DC bus from one subsystem to another.
One solution to mitigate above problem is the use of varistors in combination with RC snubbers which are devoted to absorb the energy associated with the DC bus current when a controllable switch opens during the fault. However, many of these solutions involve utilizing a DC circuit breaker.
Therefore, there still exists a need for a compact and a reliable system for transmitting electric power to subsea or marine equipment.